Micropumps are widely used in the Bio-MEMS technology, such as microfluidic sensors, microfluidic analysis chips, or microfluidic cellular chips. Take microfluidic analysis chip as an example. Micropumps can be used in sample pre-processing, mixing, transmission, isolation, and detection. There are numerous methods to fabricate a micropump. These methods are generally categorized as: bubble pumps, membrane pumps (compressed-air-driven, thermal-pressure-driven, piezoelectric-driven, static-electric-driven, dual-metal-driven, shape memory alloy (SMA) driven, and electromagnetic-driven), diffusion pumps, rotation pumps, electro-fluidic pumps, and electro-osmotic pumps.
In 1988, Van Lintel et. al. used piezoelectric material-driven membrane to fabricate micropumps. In U.S. Pat. No. 6,010,316, Haller et. al. teaches a micropump as shown in FIG. 1, in which a fluid is pumped by the interaction of longitude acoustic waves and the fluid in the microchannel. The micropump has an acoustical transducer 105 responsive to a high-frequency input and directing a longitudinal acoustic wave into the channel 106 which induces a pressure gradient. The fluid in the channel flows in the direction of travel of the acoustic wave in the channel. In U.S. Pat. No. 0,196,900, Chuang et. al. discloses a hydrogel-driven micropump using electrophoresis to drive charged ions to move under the high electro-pressure. In 2000, Wallace used an electro-osmotic pump to drive the flow of the fluid by external driving voltage and the distribution of fluid charges. WO 03/008102 disclosed a microfluidic gravity pump with constant flow rate utilizing the height difference between connected two fluid containers, 401 and 402, as shown in FIG. 2.
Prior art micropumps are numerous. However, the primary object of a micropump is to provide a driving force for the microfluid in a microchannel to flow in a specified direction. Thereby, it is important that a practical micropump should be low in energy-consumption, low in manufacturing cost and free-of-pollution.